System for tail gas treatment of sulfur recovery units

ABSTRACT

A process for recovering sulfur from a tail gas stream comprising the steps of providing a tail gas stream to a chemical looping combustion (CLC) unit, the tail gas stream comprising a sulfide component, providing an oxygen carrier to the CLC unit, the oxygen carrier comprising a calcium carbonate, providing an air stream to the CLC unit, the air stream comprising oxygen, and reacting the sulfide component in the CLC unit with the calcium compound and the air to produce a product effluent, the product effluent comprising calcium sulfate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of claims priority from U.S.Non-Provisional application Ser. No. 15/832,136 filed on Dec. 5, 2017.For purposes of United States patent practice, this applicationincorporates the contents of the non-provisional application byreference in its entirety.

TECHNICAL FIELD

Disclosed are systems and methods for removing sulfur compounds. Morespecifically, disclosed are systems and methods for removing sulfurcompounds from a tail gas stream of a sulfur recovery unit.

BACKGROUND

The removal of sour gas or acid gas components such as hydrogen sulfide(H₂S), carbon dioxide (CO₂), carbonyl sulfide (COS), carbon disulfide(CS₂) and mercaptans (RSH) from gas and liquid hydrocarbon streams is aprocess requirement in many parts of the hydrocarbon processingindustry. Increasingly stringent environmental restrictions coupled withthe need to process natural gas and crude oil with significant levels ofsulfur requires sulfur recovery processes that can achieve high levelsof conversion of hydrogen sulfide to elemental sulfur. The most commonconversion method used is the Claus process. Approximately 90 to 95percent (%) of recovered sulfur is produced by the Claus process.

The Claus process or Claus unit includes a thermal stage and a catalyticstage. The thermal stage can include a furnace, where hydrogen sulfideis reacted with oxygen to form sulfur dioxide (SO₂) at hightemperatures, such as temperatures greater than 800 degrees Celsius (degC.). Hydrogen sulfide and sulfur dioxide can react in the thermal stageto form elemental sulfur and steam. The process gases from the thermalstage can be cooled and the elemental sulfur can be separated from theother gases. The separated process gases can be routed to the catalyticstage. In the catalytic stage, catalytic reactions occur at lowertemperatures (as compared to the thermal stage) in two to threecatalytic reactors, such that further elemental sulfur recovery isachieved. The Claus process typically recovers 95% to 97% of thehydrogen sulfide in the feed stream.

The Claus process is less efficient when the feed stream containshydrogen sulfide concentrations less than 40% and can require oxygenenriched air or additional thermal and catalytic stages to reach highersulfur recovery. Additionally, low hydrogen sulfide concentrations canrequire reactors with larger volumes to handle the oxygen concentrationin the air.

A treatment unit can be placed upstream of the Claus unit to firstrecover hydrogen sulfide from a sour gas. The tail gas from thecatalytic stage can be treated to increase sulfur recovery. Clausreaction thermodynamics allows only 70% of the sulfur to be recovered inthe thermal stage and catalytic stages and subsequently tail gastreatment stages are required to reach target sulfur recovery. Selectionof an appropriate and cost effective tail gas treatment process tofollow existing Claus plants is a challenge facing refiners and naturalgas plant owners around the world.

SUMMARY

Disclosed are systems and methods for removing sulfur compounds. Morespecifically, disclosed are systems and methods for removing sulfurcompounds from a tail gas stream of a sulfur recovery unit.

In a first aspect, a process for recovering sulfur from a tail gasstream is provided. The process includes the steps of providing a tailgas stream to a chemical looping combustion (CLC) unit, where the tailgas stream includes a sulfide component, providing an oxygen carrier tothe CLC unit, where the oxygen carrier includes calcium carbonate,providing an air stream to the CLC unit, where the air stream includesoxygen, and reacting the sulfide component in the CLC unit with thecalcium carbonate and the oxygen to produce a product effluent, theproduct effluent includes calcium sulfate.

In certain aspects, the process further includes the steps ofintroducing the oxygen carrier to an air reactor of the CLC unit,introducing the air stream to the air reactor of the CLC unit, allowingthe calcium carbonate to decompose in the air reactor to produce an airreactor effluent that includes calcium oxide, introducing the airreactor effluent to an air reactor separator that includes a solid-gasseparation unit, separating calcium oxide from the air reactor effluentin the air reactor separator to produce an air reactor exhaust and anair reactor discharge, where the air reactor discharge includes thecalcium oxide, introducing the air reactor discharge to a fuel reactorof the CLC unit, introducing the tail gas stream to the fuel reactor,reacting the calcium oxide and the hydrogen sulfide to produce a fuelreactor effluent, the fuel reactor effluent includes calcium sulfide andcalcium carbonate, introducing the fuel reactor effluent to a fuelreactor separator that includes a solid-gas separation unit, separatingthe calcium sulfide and calcium carbonate from the fuel reactor effluentin the fuel reactor separator to produce a flue gas exhaust and a fuelreactor discharge, where the fuel reactor discharge includes the calciumsulfide and calcium carbonate, introducing the fuel reactor discharge tothe air reactor, reacting the calcium sulfide and the oxygen in the airreactor to produce calcium sulfate, and withdrawing a product effluentfrom the air reactor discharge, the product effluent includes a fractionof the calcium sulfate. In certain aspects, the fuel reactor is operatedat a fuel reaction pressure of atmospheric pressure, and further whereinthe fuel reactor is operated at a fuel reaction temperature of 650 degC. In certain aspects, the air reactor is operated at an air reactionpressure of atmospheric pressure, and further wherein the air reactor isoperated at an air reaction temperature of 900 deg C. In certainaspects, the air reactor is a fluidized bed reactor packed with calciumcarbonate, and further wherein the fuel reactor is a fluidized bedreactor packed with calcium carbonate.

In certain aspects, the process further includes the steps ofintroducing the oxygen carrier to a calciner unit of the CLC unit,calcining the calcium carbonate in the oxygen carrier to produce acalciner effluent that includes calcium oxide, introducing the calcinereffluent to a calciner separator, the calciner separator includes asolid-gas separation unit, separating the calcium oxide from thecalciner effluent in the calciner separator to produce a calcinerexhaust and a calciner discharge, introducing the calciner discharge toa fuel reactor of the CLC unit, introducing the tail gas stream to thefuel reactor, reacting the calcium oxide and the hydrogen sulfide toproduce a fuel reactor effluent, where the fuel reactor effluentincludes calcium sulfide and calcium carbonate, introducing the fuelreactor effluent to a fuel reactor separator, the fuel reactor separatorincludes a solid-gas separation unit, separating the calcium sulfide andcalcium carbonate from the fuel reactor effluent in the fuel reactorseparator to produce a flue gas exhaust and a fuel reactor discharge,where the fuel reactor discharge includes the calcium sulfide andcalcium carbonate, introducing the fuel reactor discharge to an airreactor of the CLC unit, reacting the calcium sulfide and the oxygen inthe air reactor to produce an air reactor effluent, the air reactoreffluent includes calcium sulfate, introducing the air reactor effluentto an air reactor separator, the air reactor separator includes asolid-gas separation unit, separating calcium oxide from the air reactoreffluent in the air reactor separator to produce an air reactor exhaustand an air reactor outlet, where the air reactor outlet includes thecalcium sulfate, withdrawing a product effluent from the air reactoroutlet, the product effluent includes a fraction of the calcium sulfate.In certain aspects, the calciner unit is operated at a calciner reactionpressure of atmospheric pressure, and further wherein the calciner unitis operated at a calciner reaction temperature of 900 deg C.

In certain aspects, the process further includes the steps ofintroducing the oxygen carrier to a calciner unit of the CLC unit,calcining the calcium carbonate in the oxygen carrier to produce acalciner effluent, calciner effluent includes calcium oxide, introducingthe calciner effluent to a calciner separator, the calciner separatorincludes a solid-gas separation unit, separating the calcium oxide fromthe calciner effluent in the calciner separator to produce a calcinerexhaust and a calciner discharge, diverting a portion of the calcinerdischarge to produce a calciner slipstream, introducing the calcinerdischarge to a fuel reactor of the CLC unit, introducing the tail gasstream to the fuel reactor, reacting the calcium oxide and the hydrogensulfide to produce a fuel reactor effluent, the fuel reactor effluentincludes calcium sulfide and calcium carbonate, introducing the fuelreactor effluent to a fuel reactor separator, the fuel reactor separatorincludes a solid-gas separation unit, separating the calcium sulfide andcalcium carbonate from the fuel reactor effluent in the fuel reactorseparator to produce a flue gas exhaust and a fuel reactor discharge,where the fuel reactor discharge includes the calcium sulfide andcalcium carbonate, introducing the flue gas exhaust and the calcinerslipstream to a reducing reactor of the CLC unit, reacting the calciumoxide and hydrogen sulfide in the reducing reactor to produce a reducingreactor effluent, separating the reducing reactor effluent in a reducingreactor separator to produce an exhaust gases stream and a reducingreactor discharge, the reducing reactor separator includes a solid-gasseparation unit, introducing the reducing reactor discharge to thecalciner unit, introducing the fuel reactor discharge to an air reactorof the CLC unit, reacting the calcium sulfide and the oxygen in the airreactor to produce an air reactor effluent, the air reactor effluentincludes calcium sulfate, introducing the air reactor effluent to an airreactor separator, the air reactor separator includes a solid-gasseparation unit, separating calcium oxide from the air reactor effluentin the air reactor separator to produce an air reactor exhaust and anair reactor discharge, where the air reactor discharge includes thecalcium sulfate, withdrawing a product effluent from the air reactordischarge, the product effluent includes a fraction of the calciumsulfate. In certain aspects, the fuel reactor is operated at a fuelreaction pressure of atmospheric pressure, and further wherein the fuelreactor is operated at a fuel reaction temperature of 830 deg C. Incertain aspects, the reducing reactor is operated at a reducing pressureof atmospheric pressure, and further wherein the reducing reactor isoperated at a reducing temperature of 650 deg C.

In certain aspects, the process further includes the steps ofintroducing an acid gas stream to a sulfur recovery unit, the acid gasstream includes hydrogen sulfide, introducing a sulfur recovery unit(SRU) air stream to the sulfur recovery unit, where the SRU air streamincludes oxygen, introducing an SRU fuel stream to the sulfur recoveryunit, and reacting an amount of the hydrogen sulfide in the sulfurrecovery unit with oxygen to produce an elemental sulfur stream and thetail gas stream.

In certain aspects, the process further includes the steps ofintroducing a sour gas feed to a gas sweetening unit, the sour gas feedincludes hydrogen sulfide, product gases, and combinations of the same,separating the hydrocarbons in the gas sweetening unit to produce asales gas stream, the sales gas stream includes the product gases,collecting the hydrogen sulfide and the other gases in the acid gasstream, introducing the acid gas stream to a sulfur recovery unit, theacid gas stream includes hydrogen sulfide, introducing a sulfur recoveryunit (SRU) air stream to the sulfur recovery unit, the SRU air streamincludes oxygen, introducing an SRU fuel stream to the sulfur recoveryunit, and reacting an amount of the hydrogen sulfide in the sulfurrecovery unit with oxygen to produce an elemental sulfur stream and thetail gas stream.

In certain aspects, the process further includes the steps ofintroducing a sour gas feed to a gas sweetening unit, the sour gas feedincludes hydrogen sulfide, product gases, and combinations of the same,separating the hydrocarbons in the gas sweetening unit to produce asales gas stream, the sales gas stream includes the product gases,collecting the hydrogen sulfide and the other gases in the acid gasstream, introducing the acid gas stream to a membrane unit, the membraneunit includes a hydrogen sulfide selective membrane, separating thehydrogen sulfide from the acid gas stream in the membrane unit toproduce a hydrogen sulfide rich acid gas and a hydrogen sulfide leanacid gas, where the hydrogen sulfide rich acid gas includes hydrogensulfide, introducing the hydrogen sulfide rich acid gas to a sulfurrecovery unit, introducing a sulfur recovery unit (SRU) air stream tothe sulfur recovery unit, the SRU air stream includes oxygen,introducing an SRU fuel stream to the sulfur recovery unit, reacting anamount of the hydrogen sulfide in the sulfur recovery unit with oxygento produce an elemental sulfur stream and a tail gas stream, mixing thetail gas stream and the hydrogen sulfide lean acid gas to produce amixed gas stream, and introducing the mixed gas stream to the CLC unit.

In second aspect, a system for recovering sulfur from a tail gas streamis provided. The system includes an air reactor, where the air reactoroperates at an air reaction temperature and an air reaction pressure,where the air reactor includes a fluidized bed reactor, where thefluidized bed includes calcium carbonate, an air reactor separatorfluidly connected to the air reactor and a fuel reactor, the air reactorseparator includes a solid-gas separation unit, the fuel reactor fluidlyconnected to the air reactor separator, where the fuel reactor operatesat a fuel reaction temperature and fuel reaction pressure, where thefuel reactor includes a fluidized bed reactor, where the fluidized bedincludes calcium carbonate, and a fuel reactor separator fluidlyconnected to the fuel reactor and the air reactor, the fuel reactorseparator includes a solid-gas separation unit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the scope willbecome better understood with regard to the following descriptions,claims, and accompanying drawings. It is to be noted, however, that thedrawings illustrate only several embodiments and are therefore not to beconsidered limiting of the scope as it can admit to other equallyeffective embodiments.

FIG. 1 is a process diagram of an embodiment of the sulfur recoveryprocess.

FIG. 2 is a process diagram of an embodiment of the sulfur recoveryprocess.

FIG. 3 is a process diagram of an embodiment of the sulfur recoveryprocess.

FIG. 4 is a process diagram of an embodiment of the sulfur recoveryprocess.

FIG. 5 is a process diagram of an embodiment of the sulfur recoveryprocess.

FIG. 6 is a process diagram of an embodiment of the sulfur recoveryprocess.

DETAILED DESCRIPTION

While the scope of the apparatus and method will be described withseveral embodiments, it is understood that one of ordinary skill in therelevant art will appreciate that many examples, variations andalterations to the apparatus and methods described here are within thescope and spirit of the embodiments.

Accordingly, the embodiments described are set forth without any loss ofgenerality, and without imposing limitations, on the embodiments. Thoseof skill in the art understand that the scope includes all possiblecombinations and uses of particular features described in thespecification.

The embodiments of the systems and methods of sulfur recovery describedhere are directed to the use of a chemical looping combustion (CLC)process to treat a tail gas stream from a Claus process. In a CLCprocess, a fuel reacts with a metal oxide in the reducer, the fuelreactor, so that the metal oxide is reduced to metal. Other reactionproducts in the reducer include carbon dioxide and steam. The metalexits the reducer and enters the combustor, the air reactor, where themetal reacts with air to regenerate the metal oxide. The metal oxides isthen recycled back to the reducer. The heat of oxidation is carried bythe oxidized metal and the high-temperature spent air from the airreactor. The spent air is used to produce steam that can be used asutility or to drive steam turbines for electricity generation. Thereaction products depend on the reactants, the operating conditions, andthe specific metal oxide employed in each reactor.

Advantageously, the systems and methods described address both feedstreams with lower hydrogen sulfide concentrations and the need for tailgas treatment to meet environmental regulations. Advantageously, thesystems and methods reduce the size of equipment across the entiresulfur recovery system. Advantageously, the systems and methodsdescribed here can be added to existing Claus processes. Advantageously,the systems and methods described here have increased efficiencycompared to the conventional Claus process. Advantageously, the systemsand methods described provide enhanced operation flexibility compared toconventional sulfur recovery processes. The systems and methods forsulfur recover provide enhanced operational flexibility compared toconventional processes. The systems and methods allow operation of theClaus unit at lower sulfur recovery levels, such as around 95%, whilestill meeting the emissions regulation limits.

As used throughout, “efficient” or “efficiency” refers to the energyconsumption required to clean up the tail gas from a sulfur recoveryunit.

As used throughout, “loop” or “loops” refers to the configuration ofreactors in chemical looping combustion unit. The combination of fuelreactor, air reactor, calciner, reducing reactor, and combinations ofthe same.

As used throughout, “sulfur-containing compounds” includessulfur-containing gaseous compounds other than hydrogen sulfide, sulfurdioxide, and elemental sulfur, naturally occurring or produced as partof an industrial process that can be removed from a gas stream in asulfur recovery unit. Examples of sulfur-containing compounds caninclude carbonyl sulfide, carbon disulfide, sulfur trioxide, sulfuroxides (SOx), and combinations of the same.

As used throughout, “product gases” refers to gases which can be treatedfor sale or other industrial use. Examples of product gases includenatural gas, light hydrocarbons, such as methane and ethane, air, andcombinations of the same.

As used throughout, “sour gases” refers gases containing hydrogensulfide and carbon dioxide.

As used throughout, “calcining” or “calcination” refers to removal ofcarbon dioxide in an endothermic reaction from calcium carbonateresulting in a calcium oxide product.

Referring to FIG. 1, a CLC unit suitable for use in the sulfur recoveryprocess is described. CLC unit 10 contains a minimum of two fluidizedbed reactors interconnected using loops. Oxygen carrier 105 can beintroduced to air reactor 14 of CLC unit 10. Oxygen carrier 105 caninclude any oxygen carrier that reacts with sulfur. Examples of oxygencarriers can include calcium (Ca), iron (Fe), nickel (Ni), manganese(Mn), copper (Cu), and combinations of the same. In at least oneembodiment, the oxygen carrier includes calcium. In at least oneembodiment, the oxygen carrier includes calcium in the form of calciumcarbonate (CaCO₃). In at least one embodiment, the oxygen carrierincludes calcium in the form of calcium oxide (CaO). Advantageously, theuse of calcium-based particles results in the sulfur compounds beingtrapped such that the calcium-based particles produce calcium-sulfurproducts. The oxygen in oxygen carrier 105 can be in a solid form. In atleast one embodiment, oxygen carrier 105 is continuously introduced toCLC unit 10. In at least one embodiment, oxygen carrier 105 isintroduced on an as needed-basis.

Air stream 115 can be introduced to air reactor 14 of CLC unit 10. Airstream 115 can be any source of air. Air stream 115 can include air,oxygen-enriched air, oxygen, or combinations of the same.

Air reactor 14 can be any type of bed reactor capable of supportingreactions containing oxygen, sulfur, and metals. In at least oneembodiment, air reactor 14 is a fluidized bed reactor. The oxygencarrier can be loaded into air reactor 14 prior to the unit being placedin production. Air reactor 14 can operate at an air reactiontemperature, an air reaction pressure, and an air reaction residencetime. The air reaction temperature can be between 600 deg C. and 1300deg C., alternately at or less than 900 deg C., and alternately between500 deg C. and 890 deg C. Advantageously, maintaining an air reactiontemperature at or less than 900 deg C. results in the oxidation of theoxygen carrier while reducing or suppressing the formation of nitrogenoxides (NO_(x)). The reactions in air reactor 14 can be exothermic. Theair reaction pressure can be atmospheric pressure, alternately between 1bar (100 kPa) and 10 bar (1000 kPa), and alternately between 1 bar (100kPa) and 3 bar (300 kPa). The air reaction residence time can be between1 second and 600 seconds and alternately between 80 seconds and 200seconds.

Tail gas stream 100 can be introduced to fuel reactor 12 of CLC unit 10.Tail gas stream 100 can be the tail gas from any process unit containinghydrogen sulfide, sulfur dioxide, or combinations of the same. In atleast one embodiment, tail gas stream 100 is produced by a Clausprocess.

Fuel stream 125 can be introduced to fuel reactor 12 of CLC unit 10.Fuel stream 125 can be any source of fuel that can be used in fuelreactor 12 to maintain the temperature. The reactions occurring in CLCunit 10 are endothermic requiring the addition of fuel to maintain thetemperature. Examples of the fuel suitable for use in fuel stream 125include combustible gases, liquid fuels, and solid fuels. In at leastone embodiment, fuel stream 125 provides a combustible gas to maintainthe temperature in fuel reactor 12. Examples of the combustible gas infuel stream 125 include methane, carbon monoxide, hydrogen, fuel gases,and combinations of the same. In at least one embodiment, fuel stream125 includes a combustible gas and has reduced complexity as compared tothe use of a liquid fuel or solid fuel.

Fuel reactor 12 can operate at a fuel reaction temperature, a fuelreaction pressure, and a fuel reaction residence time. The fuel reactiontemperature can be equal to or less than 900 deg C., alternately between850 deg C. and 900 deg C., alternately between 800 deg C. and 850 degC., alternately between 750 deg C. and 800 deg C., alternately between700 deg C. and 750 deg C., alternately between 650 deg C. and 700 degC., alternately equal to or less than 600 deg C. In at least oneembodiment the fuel reaction temperature is 650 deg C. The fuel reactionpressure can be atmospheric pressure. The fuel reaction residence timecan be between 1 second and 700 seconds and alternately between 50seconds and 400 seconds.

The following describes the process and reactions occurring in CLC unit10 when the oxygen carrier is calcium carbonate. While the process andreactions will be described along a linear path beginning with theoxygen carrier, one of skill in the art will understand that after astart-up period, the reactants and products will circulate through theCLC unit in a continuous loop except those products withdrawn asdescribed. To the extent a stream is described as containing orincluding specific components, it is understood that any of thecomponents (reactants or products listed in reactions 1-38) can bepresent and only certain components are noted. Multiple and competingreactions, as described, can be occurring simultaneously in bothreactors.

Oxygen carrier 105 includes calcium in the form of calcium carbonate. Inair reactor 14, the calcium carbonate decomposes to form calcium oxide(CaO) and carbon dioxide according to the following equation:CaCO₃→CaO+CO₂  reaction 1

Reaction 1 is an endothermic reaction with a change in enthalpy (ΔH) ofpositive 178 kilojoules per mole (kJ/mol). While individual reactions inair reactor 14 can be endothermic, the overall change in enthalpy in airreactor 14 is negative (exothermic). The calcium oxide is in solid form.Air reactor effluent 111 containing the products formed in air reactor14 are introduced to air reactor separator 11. The solid products,including the calcium oxide are entrained in the gases in air reactoreffluent 111 and carried to air reactor separator 11.

Air reactor separator 11 can be any type of separation unit capable ofseparating solids from gases. In at least one embodiment air reactorseparator 11 is a cyclone separation unit. The gases separated in airreactor separator 11 exit the system as air reactor exhaust 140. Airreactor exhaust 140 can include carbon dioxide, nitrogen, argon, andcombinations of the same. In at least one embodiment, air reactorexhaust 140 is in the absence of nitrogen oxides. Although described asa separate unit, one of skill in the art understands that the airreactor separator can be physically connected to the air reactor or bebuilt into the air reactor.

The solids separated in air reactor separator 11 exit as air reactordischarge 114 and can be introduced to fuel reactor 12. Air reactorseparator 11 and fuel reactor 12 can be designed and arranged to aid intransport of the solids from air reactor separator 11 to fuel reactor 12by air reactor discharge 114. In at least one embodiment, air reactordischarge 114 contains only solids. In fuel reactor 12, the calciumoxide can react with the hydrogen sulfide in tail gas stream 100 toproduce calcium sulfide (CaS) and water (H₂O) according to the followingreaction:CaO+H₂S→CaS+H₂O  reaction 2

Reaction 2 is exothermic with a ΔH of negative 59.44 kJ/mol. Additionalreactions that can occur in fuel reactor 12, can include:CaO+CO₂→CaCO₃  reaction 3CaO+SO₂+0.5O₂↔CaSO₄  reaction 4CaO+SO₂↔CaSO₃  reaction 5CaO+SO₃↔CaSO₄  reaction 6CaCO₃+SO₂+0.5O₂↔CaSO₄+CO₂  reaction 7CaCO₃+H₂S↔CaS+CO₂+H₂O  reaction 8CaSO₄+4CH₄↔4CO+8H₂+CaS  reaction 9CaSO₄+3H₂S↔CaO+3H₂O+0.5S₈  reaction 10CaSO₄+CO ↔CaO+SO₂+CO₂  reaction 11CaSO₃+0.5O₂↔CaSO₄  reaction 12CaS+1.5O₂↔CaO+SO₂  reaction 13CaS+3CaSO₄↔4CaO+4SO₂  reaction 14CaS+2SO₂↔CaSO₄+S₂  reaction 15CaS+CO₂↔CaO+COS  reaction 16CaS+2CO₂↔CaCO₃+COS  reaction 17CaS+3CO₂↔CaO+3CO+SO₂  reaction 18CaS+4CO₂↔CaSO₄+4CO  reaction 192CaS+CO₂↔CS₂+CaO  reaction 20CaS+3H₂O ↔CaO+3H₂+SO₂  reaction 21CaS+COS↔CS₂+2CaO  reaction 22H₂S+0.5O₂↔H₂O+1/n S_(n)  reaction 23H₂S+1.5O₂↔H₂O+SO₂  reaction 24H₂S+CO ↔COS+H₂  reaction 25H₂S+CO₂↔COS+H₂O  reaction 262H₂S+CO₂↔CS₂+2H₂O  reaction 272H₂S+3O₂↔2S O₂+2H₂O  reaction 282H₂S+SO₂↔3S+2H₂O  reaction 29S₂+CO₂↔COS+SO₂  reaction 30S+H₂↔H₂S  reaction 31SO₂+3H₂↔2H₂O+H₂S  reaction 32CH₄+SO₂+0.5O₂↔COS+2H₂O  reaction 33CH₄+4S↔CS₂+2H₂S  reaction 34COS+2O₂↔CO₂+SO₂  reaction 35COS+H₂S↔CS₂+H₂O  reaction 36

where O₂ is oxygen, SO₃ is sulfur trioxide, CaSO₃ is calcium sulfite,CaSO₄ is calcium sulfate, CO is carbon monoxide, CH₄ is methane, H₂ ishydrogen, and S_(n) refers to elemental sulfur, where n=a number between1 and 8 inclusive. It should be noted that sulfur dioxide can react withcalcium oxide to produce calcium sulfite and calcium sulfate, such as inreactions 4-6.

While individual reactions in fuel reactor 12 can be exothermic, theoverall change in enthalpy in fuel reactor 12 is positive (endothermic).The total change in enthalpy is limited by the amount of fuel in tailgas stream 100 and the amount of fuel in fuel stream 125.

Fuel reactor effluent 113 can contain calcium sulfide (from reaction 2)and calcium carbonate (from reaction 3). Fuel reactor effluent 113 exitsfuel reactor 12 and is introduced to fuel reactor separator 13.

Fuel reactor separator 13 can be any type of separation unit capable ofseparating solids from gases. In at least one embodiment fuel reactorseparator 13 is a cyclone separation unit. The gases separated in fuelreactor separator 13 exit the system as flue gas exhaust 120. Flue gasexhaust 120 can contain steam and flue gases. Flue gases can includenitrogen, carbon dioxide, oxygen, particulate matter, carbon monoxide,nitrogen oxides, sulfur oxides, and combinations of the same.

The remaining gases and solids, including calcium sulfide and calciumcarbonate exit the fuel reactor separator as fuel reactor discharge 112.Fuel reactor discharge 112 can be introduced to air reactor 14. Fuelreactor separator 13 and air reactor 14 can be designed and arranged toaid and facilitate transport of the solids from fuel reactor separator13 to air reactor 14 by fuel reactor discharge 112. In at least oneembodiment, fuel reactor discharge 112 contains only solids. In airreactor 14, the calcium sulfide can be oxidized with oxygen from airstream 115 to form calcium sulfate (CaSO₄) according to the followingreactions:CaS+2O₂→CaSO₄  reaction 37CaS+2(1+x)(O₂+3.76N₂)→CaSO₄+2xO₂=2(1+x)*3.76N₂  reaction 38

where N₂ is nitrogen.

The calcium sulfate can be in the form of solid particles. The calciumsulfate can be entrained in air reactor effluent 111 and introduced toair reactor separator 11. The calcium sulfate can exit air reactorseparator 11 in air reactor discharge 114 and be introduced to fuelreactor 12.

A slipstream can be removed from air reactor discharge 114 as producteffluent 110. Any means of separating a fraction of solids can be usedto remove product effluent 110. In at least one embodiment, the means ofseparating a fraction of solids can be a valve. Product effluent 110 caninclude a fraction of the solids in air reactor discharge 114. Thesolids in product effluent 110 can include calcium sulfate, calciumoxide, calcium carbonate, and combinations of the same. In at least oneembodiment, product effluent 110 includes calcium sulfate. The fractionof the solids removed in product effluent 110 from air reactor discharge114 can be between 10 weight percent (wt %) and 30 wt %, alternatelybetween 10 wt % and 25 wt %, alternately between 10 wt % and 20 wt %,alternately between 10 wt % and 15 wt %, and alternately between 12 wt %and 15 wt %. The flow rate of product effluent can be regulated throughan instrumentation control loop to adjust the temperature in fuelreactor 12. The instrumentation control loop can include a valve thatopens to allow flow in product effluent 110 and a temperature gauge infuel reactor 12. The calcium sulfate in product effluent 110 can be usedto produce cement.

It can be understood that reaction 1, reaction 37, and reaction 38 canoccur at the same time in air reactor 14 after tail gas stream 100 hasbeen introduced to CLC unit 10 and the reactants have completed a firstloop through air reactor 14 and fuel reactor 12. One of skill in the artwill understand that reactions 1-38 can compete with each otherdepending on the reaction kinetics of each reaction.

Referring to FIG. 2, with reference to FIG. 1, an embodiment of thechemical looping combustion unit is provided.

Oxygen carrier 105 can be introduced to calciner unit 16. Calciner unit16 can be any type of calciner unit capable of calcining calciumcarbonate. Calciner unit 16 can operate at a calciner reactiontemperature, a calciner reaction pressure, and a calciner reactionresidence time. The calciner reaction temperature can be between 800 degC. and 1300 deg C. and alternately between 850 deg C. and 950 deg C. Inat least one embodiment, the calciner reaction temperature is 900 deg C.The calciner reaction pressure can be between 1 bar (100 kPa) and 5 bar(500 kPa). The calciner reaction residence time can be between 1 secondand 600 seconds and alternately between 80 seconds and 200 seconds.

The following describes the process and reactions occurring in CLC unit10 with the inclusion of calciner unit 16, when the oxygen carrier iscalcium carbonate and with reference to FIG. 1. While the process andreactions will be described along a linear path, one of skill in the artwill understand that after a start-up period, the reactants and productswill circulate through the CLC unit in a continuous loop except thoseproducts withdrawn as described. Multiple and competing reactions, asdescribed, can be occurring simultaneously in both reactors.

In calciner unit 16, the calcium carbonate can form calcium oxide andcarbon dioxide according to reaction 1. The products can exit calcinerunit 16 as calciner effluent 217. Calciner effluent 217 can includecalcium oxide, carbon dioxide, nitrogen, and combinations of the same.Calciner effluent 217 can be introduced to calciner separator 17.

Calciner separator 17 can be any type of separation unit capable ofseparating solids from gases. In at least one embodiment calcinerseparator 17 is a cyclone separation unit. The gases separated incalciner separator 17 can exit CLC unit 10 as calciner exhaust 240.Calciner exhaust 240 can include nitrogen, carbon dioxide, oxygen, andcombinations of the same.

The solids separated in calciner separator exit as calciner discharge216. Calciner discharge 216 can include calcium oxide. Calcinerdischarge 216 can be introduced to fuel reactor 12.

Air reactor separator 11 can separate air reactor effluent 111 into airreactor exhaust 140 and air reactor outlet 214. Air reactor exhaust 140can be introduced to calciner unit 16. Air reactor outlet 214 cancontain calcium sulfate, calcium carbonate, calcium oxide, andcombinations of the same. In at least one embodiment, air reactor outlet214 can have a different composition than air reactor discharge 114,such as less calcium oxide, less calcium carbonate, and a greater amountof calcium sulfate. In at least one embodiment, the system describedwith reference to FIG. 2 can result in increased oxidation and reducedtemperatures as compared to the system as described with reference toFIG. 1. Air reactor outlet 214 can be introduced to calciner unit 16.Product effluent 110 can be separated from air reactor outlet 214.

The addition of the calciner unit enables flexible operation of the CLCunit by providing the ability to adjust the operating conditions in eachunit. By being able to adjust the operating conditions in the units, thesystem experiences reduced losses of calcium oxide and enhanced systemenergy efficiency.

Referring to FIG. 3, with reference to FIGS. 1 and 2, an embodiment ofCLC unit 10 is provided that includes reducing reactor 18. The followingdescribes the process and reactions occurring in CLC unit 10 with theinclusion of calciner unit 16 and reducing reactor 18, when the oxygencarrier is calcium carbonate and with reference to FIG. 1. While theprocess and reactions will be described along a linear path, one ofskill in the art will understand that after a start-up period, thereactants and products will circulate through the CLC unit in acontinuous loop except those products withdrawn as described. Multipleand competing reactions, as described, can be occurring simultaneouslyin both reactors.

In the embodiment shown with respect to FIG. 3, fuel reactor separator13 separates air reactor effluent 113 into flue gas exhaust 120 and fuelreactor discharge 112. In an embodiment of CLC unit 10 that includesreducing reactor 18, fuel reactor 12 can operate at a fuel reactiontemperature of 830 deg C. and a fuel reaction pressure of atmosphericpressure. Advantageously, operating fuel reactor 12 at a fuel reactiontemperature of 830 deg C. results in calcium oxide selectively reactingwith hydrogen sulfide, reaction 2. The fuel reaction temperature of 830deg C. minimizes the carbon dioxide carbonation reaction, shown asfollows:CaO+CO₂→CaCO₃  reaction 39Flue gas exhaust 120 can be introduced to reducing reactor 18.

Calciner slipstream 316 can be separated from calciner discharge 216.Calciner slipstream 316 can include a fraction of the solids in calcinerdischarge 216. The solids in calciner slipstream 316 can include calciumsulfate, calcium oxide, calcium carbonate, and combinations of the same.In at least one embodiment, calciner slipstream 316 includes calciumsulfate. The fraction of the solids removed in calciner slipstream 316from calciner discharge 216 can be between 5 weight percent (wt %) and20 wt %, alternately between 8 wt % and 15 wt %, and alternately between10 wt % and 12 wt %. The fraction of solids removed in calcinerslipstream 316 can be controlled by an instrumentation loop thatcontrols the temperature of flue exhaust 120. The temperature of flueexhaust 120 is indicative of the operating conditions and the extent ofconversion in reducing reactor 18. Based on the temperature of flueexhaust 120, the amount of solids entering reducing reactor 18 can becontrolled by the weight in calciner slipstream 316. Calciner slipstream316 can be introduced to reducing reactor 18. Reactions 2-36 occur inreducing reactor 18 with reactants from calciner slipstream 316 and fluegas exhaust 120.

Reducing reactor 18 can operate at a reducing temperature, a reducingpressure, and a reducing reactor residence time. The reducingtemperature can be equal to or less than 900 deg C., alternately between850 deg C. and 900 deg C., alternately between 800 deg C. and 850 degC., alternately between 750 deg C. and 800 deg C., alternately between700 deg C. and 750 deg C., alternately between 650 deg C. and 700 degC., alternately equal to or less than 600 deg C. In at least oneembodiment, the reducing temperature in reducing reactor 18 is 650 degC. The reducing pressure can be atmospheric pressure. The reducingreactor residence time can be between 1 second and 700 seconds andalternately between 50 seconds and 400 seconds. Operating reducingreactor 18 at temperatures lower than fuel reactor 12 increases theefficiency of reducing reactor 18 and suppresses side reactions.Reducing reactor effluent 318 can be introduced to reducing reactorseparator 19.

Reducing reactor separator 19 can be any type of separation unit capableof separating solids from gases. In at least one embodiment reducingreactor 19 is a cyclone separation unit. The gases separated in reducingreactor separator 19 exit CLC unit 10 as exhaust gases stream 320.Exhaust gases stream 320 can include steam and trace amounts of hydrogensulfide. The trace amounts of hydrogen sulfide level in exhaust gasesstream 320 can be less than 1 part-per-million by volume (ppmv).Reducing reactor discharge 319 contains the solids separated fromreducing reactor effluent 318. Reducing reactor discharge 319 caninclude calcium carbonate, calcium sulfide, and combinations of thesame. Reducing reactor discharge 319 can be introduced to calciner unit16. Purge stream 300 can be withdrawn from reducing reactor discharge319. Purge stream 300 can include a fraction of the solids in reducingreactor discharge 319. The solids in purge stream 300 can includecalcium sulfate, calcium oxide, calcium carbonate, and combinations ofthe same. In at least one embodiment, purge stream 300 includes calciumsulfate, calcium oxide, and combinations of the same. The fraction ofthe solids removed in purge stream 300 from reducing reactor discharge319 can be between 5 weight percent (wt %) and 20 wt %, alternatelybetween 8 wt % and 15 wt %, and alternately between 10 wt % and 12 wt %.The combination of fuel reactor 12 and reducing reactor 18 providesbetter control of the reaction conditions in each reactor, allowing thereaction conditions in each reactor to foster specific reactions toproduce a purer product.

Employing reducing reactor 18 as part of CLC unit 10 allows CLC unit 10to achieve greater than 99.5 wt % recovery of sulfur from hydrogensulfide. Advantageously, the addition of reducing reactor 18 minimizesthe need for solids circulation. In an ideal operating environment, theneed for solids circulation would be eliminated as only calcium sulfatewould be produced from CLC unit 10 with the addition of reducing reactor18; in a real operating environment, the conversion can bethermodynamically limited requiring re-circulation of a minimal amountof solids.

Referring to FIG. 4, with reference to FIG. 1, an embodiment of a sulfurrecovery process employing a CLC unit is provided. Acid gas stream 400is introduced to sulfur recovery unit 40 along with sulfur recovery unit(SRU) fuel stream 405 and SRU air stream 415. Acid gas stream 400 can beany source of acid gas that comprises hydrogen sulfide. In at least oneembodiment, acid gas stream 40 has a concentration of hydrogen sulfidebetween 25 wt % and 75 wt %. In at least one embodiment, acid gas stream400 can include sulfur dioxide, hydrogen sulfide, carbon dioxide,sulfur-containing compounds, and combinations of the same.

SRU fuel stream 405 can be any source of fuel gas suitable forincreasing the temperature of the combustion furnace (not shown) insulfur recovery unit 40. SRU air stream 415 can be any source of oxygencontaining gas suitable for use in the combustion furnace of sulfurrecovery unit 40. SRU air stream 415 can include air, oxygen,oxygen-enriched air, and combinations of the same.

In sulfur recovery unit 40, the hydrogen sulfide in acid gas stream 400and oxygen in SRU air stream 415 react to produce elemental sulfurstream 410 and tail gas stream 100. Elemental sulfur stream 410 caninclude liquid elemental sulfur. In at least one embodiment, sulfurrecovery unit 40 can be a Claus process. Tail gas stream 100 can beintroduced to CLC unit 10.

Referring to FIG. 5, with reference to FIGS. 1 and 4, an embodiment of asulfur recovery process employing a CLC unit and a gas sweetening unitis provided. Sour gas stream 500 can be introduced to gas sweeteningunit 50. Sour gas stream 500 can be any gas stream containing sour gasesand product gases. In at least one embodiment, sour gas stream 500 caninclude methane, hydrocarbons, hydrogen sulfide, carbon dioxide, andcombinations of the same. In at least one embodiment, sour gas stream500 can include 40% by volume or less hydrogen sulfide. Sour gas stream500 is introduced to gas sweetening unit 50.

Gas sweetening unit 50 can be any unit capable of removing acid gasesfrom a gas stream. Examples of gas sweetening units can include amineunits. In at least one embodiment, gas sweetening unit 50 is an amineunit. Sour gas stream 500 is separated in gas sweetening unit 50 toproduce sales gas stream 530 and acid gas stream 400. Sales gas stream530 is a sweetened gas stream. Sales gas stream 530 can be sent forfurther processing, can be sent for storage, or can be sent fordisposal. Acid gas stream 400 can be introduced to sulfur recovery unit40.

Referring to FIG. 6, with reference to FIGS. 1, 4 and 5, an embodimentof a sulfur recovery process employing a CLC unit, a gas sweetening unitand a membrane unit is provided. Acid gas stream 400 can be introducedto membrane unit 60. Membrane unit 60 can include any membrane capableof separating hydrogen sulfide and carbon dioxide. In at least oneembodiment, membrane unit 60 includes a carbon dioxide selectivemembrane. Membrane unit 60 separates acid gas stream 400 into hydrogensulfide rich acid gas 600 and hydrogen sulfide lean acid gas 610.

Reducing the amount of carbon dioxide in hydrogen sulfide rich acid gas600 is advantageous because the carbon dioxide can act as a diluent andreduce energy needed to heat the streams to the CLC unit.

Hydrogen sulfide rich acid gas 600 can contain hydrogen sulfide, carbondioxide, and combinations of the same. In at least one embodiment,hydrogen sulfide rich acid gas 600 can contain other gases present inacid gas stream 400. Hydrogen sulfide rich acid gas 600 contains between25 wt % and 85 wt % hydrogen sulfide. Hydrogen sulfide rich acid gas 600can be introduced to sulfur recovery unit 40.

Hydrogen sulfide lean acid gas 610 can contain carbon dioxide, hydrogensulfide, and combinations of the same. Hydrogen sulfide lean acid gas610 contains between 5 wt % and 8 wt %. Hydrogen sulfide lean acid gas610 can be mixed with tail gas stream 100 to produce mixed gas 620.Mixed gas 620 can be introduced to CLC unit 10.

The sulfur recovery processes and systems described here are in theabsence of one or more thermal oxidizers. The sulfur recovery processesand systems described here are in the absence of a flue gasde-sulfurization system. Flue gas de-sulfurization systems can include aSCOT process, an ammonia process, wet scrubbing processes, and dryscrubbing processes. The addition of the CLC process can result in aClaus process that only requires two catalytic reactors in the catalyticstage. The sulfur recovery processes and systems described here are inthe absence of process units that require a feed of hydrogen gas. Thesystems and process described here are in the absence of a CLC processemploying calcium sulfate as an oxygen carrier.

EXAMPLE Example 1

The first example simulated different embodiments of CLC unit 10 asdescribed with reference to FIGS. 1, 2 and 3 in a process according toan embodiment described with reference to FIG. 5. The percentages areshown on a dry weight basis. The data are based on simulations performedusing Aspen Plus®. Stream 114 and stream 216 are introduced to fuelreactor 12 depending on the embodiment. Stream 112 is introduced to airreactor 14. Stream 214 and Stream 319 are introduced to calciner unit16.

TABLE 1 Units FIG. 1 FIG. 2 FIG. 3 Overall sulfur recovery Percent 99.9499.93 99.92 (%) Sulfur recovery in CLC % 98.8 98.78 98.57 unit 10 Stream105 kg/s 3.5 2.1 2.1 Stream 114 kg/s 52.2 N/A N/A Stream 216 kg/s N/A38.6 0.8 Stream 112 kg/s 65.3 48.2 1.0 Stream 316 kg/s N/A N/A 13.3Stream 214 kg/s N/A 2.1 N/A Stream 319 kg/s N/A N/A 24.0 Stream 115 kg/s2.6 2.6 2.6 Fuel reaction temperature deg C. 650.0 650.0 790.0 Reducingreaction deg C. N/A N/A 650.0 temperature Air reaction temperature degC. 900.0 900.0 900.0 Calciner reaction deg C. N/A 900.0 900.0temperature Fuel reactor 12 heat output MW 38.1 34.9 −18.9 Reducingreactor 18 MW N/A N/A 45.2 heat output Air reactor 14 heat output MW−57.3 −45.3 5.5 Calciner unit 16 heat output MW N/A −5.2 −46.3 Net HeatMW −19.1 −15.7 −14.5 Stream 120 Hydrogen sulfide ppm 163.8 163.8 345.0Sulfur dioxide ppm 12.7 12.7 978.0 Carbonyl sulfide ppm 0.2 0.2 13.0Carbon dioxide % 1.6 1.6 27.0 Stream 320 Hydrogen sulfide ppm N/A N/A218.3 Sulfur dioxide ppm N/A N/A 17.1 Carbonyl sulfide ppm N/A N/A 0.3Carbon dioxide % N/A N/A 2.1 Stream 140 Sulfur dioxide ppm 0.3 0.3 0.1Carbonyl sulfide ppm 0.0 0.0 0.0 Carbon dioxide % 77.9 75.2 0.0 Nitrogen% 21.9 24.6 97.9 Stream 240 Carbon dioxide % N/A 76.9 74.3 Purge Split %% 0.05000 0.05000 0.03000 Purge CaCO3 flow kg/s 0.00000 0.00000 0.00633Purge CaO flow kg/s 1.38368 0.60534 0.00000 Stream 110 kg/s 1.364201.36387 0.00031 Purge CaS flow kg/s 0.00000 0.00000 0.00002

Example 2

The second example simulated different embodiments of CLC unit 10 asdescribed with reference to FIGS. 1, 2 and 3 in a process according toan embodiment described with reference to FIG. 6. The percentages areshown on a dry weight basis. Simulated using Aspen Plus®. Stream 114 andstream 216 are introduced to fuel reactor 12 depending on theembodiment. Stream 112 is introduced to the air reactor. Stream 214 andStream 319 are introduced to calciner unit 16 depending on theembodiment.

TABLE 2 Units FIG. 1 FIG. 2 FIG. 3 Overall sulfur recovery Percent (%)99.94 99.94 99.42 Sulfur recovery in CLC unit 10 % 99.80 99.80 99.81Stream 105 kg/s 10.3 10.0 7.0 Stream 114 kg/s 57.2 N/A N/A Stream 216kg/s N/A 61.9 3.1 Stream 112 kg/s 77.8 72.3 3.9 Stream 316 kg/s N/A N/A18.5 Stream 214 kg/s N/A 10.0 N/A Stream 319 kg/s N/A N/A 33.7 Stream115 kg/s 16.6 17.6 20.0 Fuel reaction temperature deg C. 650.0 650.0900.0 Reaction temperature deg C. N/A N/A 650.0 Air reaction temperaturedeg C. 900.0 900.0 900.0 Calciner reaction temperature deg C. N/A 900.0902.0 Fuel reactor 12 heat output MW 43.9 45.0 −19.7 Reducing reactor 18heat MW N/A N/A 51.2 output Air reactor 14 heat output MW −44.0 −20.134.9 Calciner unit 16 heat output MW N/A −25.1 −58.8 Net Heat MW −0.1−0.2 7.5 Stream 120 Hydrogen sulfide Ppm 188.3 188.3 712.9 Sulfurdioxide ppm 12.7 12.7 1197.9 Carbonyl sulfide ppm 0.2 0.2 39.0 Carbondioxide % 1.6 1.6 30.4 Stream 320 Hydrogen sulfide ppm N/A N/A 188.3Sulfur dioxide ppm N/A N/A 12.7 Carbonyl sulfide ppm N/A N/A 0.2 Carbondioxide % N/A N/A 1.6 Stream 140 Sulfur dioxide ppm 0.1 0.2 0.1 Carbonylsulfide ppm 0.0 0.0 0.0 Carbon dioxide % 41.1 30.6 0.0 Nitrogen % 57.969.1 96.0 Stream 240 Carbon dioxide % N/A 39.0 32.4 Purge Split % % 0.150.15 0.05 Purge CaCO3 flow kg/s 0.00000 0.00000 0.01096 Purge CaO flowkg/s 2.7305 2.5747 0.00478 Stream 110 kg/s 7.3625 7.3627 0.00022 PurgeCaS flow kg/s 0.00000 0.00000 0.00014

Although the embodiments have been described in detail, it should beunderstood that various changes, substitutions, and alterations can bemade hereupon without departing from the principle and scope.Accordingly, the scope of the embodiments should be determined by thefollowing claims and their appropriate legal equivalents.

There various elements described can be used in combination with allother elements described here unless otherwise indicated.

The singular forms “a”, “an” and “the” include plural referents, unlessthe context clearly dictates otherwise.

Optional or optionally means that the subsequently described event orcircumstances may or may not occur. The description includes instanceswhere the event or circumstance occurs and instances where it does notoccur.

Ranges may be expressed here as from about one particular value to aboutanother particular value and are inclusive unless otherwise indicated.When such a range is expressed, it is to be understood that anotherembodiment is from the one particular value to the other particularvalue, along with all combinations within said range.

As used here and in the appended claims, the words “comprise,” “has,”and “include” and all grammatical variations thereof are each intendedto have an open, non-limiting meaning that does not exclude additionalelements or steps.

That which is claimed is:
 1. A system for recovering sulfur from a tailgas stream, the system comprising: an air reactor, where the air reactoroperates at an air reaction temperature and an air reaction pressure,where the air reactor comprises a fluidized bed reactor, where thefluidized bed comprises calcium carbonate; an air reactor separatorfluidly connected to the air reactor and a calciner separator, where theair reactor separator comprises a solid-gas separation unit; thecalciner unit fluidly connected to the air reactor separator and acalciner separator, where the calciner unit operates at a calcinerreaction temperature and a calciner reaction pressure; the calcinerseparator fluidly connected to the calciner unit and a fuel reactor,where the calciner separator comprises a solid-gas separation unit; thefuel reactor fluidly connected to the calciner separator, where the fuelreactor operates at a fuel reaction temperature and fuel reactionpressure, where the fuel reactor comprises a fluidized bed reactor,where the fluidized bed comprises calcium carbonate; and a fuel reactorseparator fluidly connected to the fuel reactor and the air reactor,where the fuel reactor separator comprises a solid-gas separation unit.2. The system of claim 1, wherein the fuel reaction pressure isatmospheric pressure, and further wherein the fuel reaction temperatureis between 800 deg C. and 850 deg C.
 3. The system of claim 1, whereinthe air reaction pressure is atmospheric pressure, and further whereinthe air reaction temperature is between 600 deg C. and 1300 deg C. 4.The system of claim 1, wherein the calciner reaction pressure isatmospheric pressure, and further wherein the calciner reactiontemperature is between 850 deg C. and 950 deg C.
 5. A system forrecovering sulfur from a tail gas stream, the system comprising: an airreactor, where the air reactor operates at an air reaction temperatureand an air reaction pressure, where the air reactor comprises afluidized bed reactor, where the fluidized bed comprises calciumcarbonate; an air reactor separator fluidly connected to the air reactorand a calciner separator, where the air reactor separator comprises asolid-gas separation unit; the calciner unit fluidly connected to theair reactor separator, where the calciner unit operates at a calcinerreaction temperature and a calciner reaction pressure; a calcinerseparator fluidly connected to the calciner unit and a fuel reactor,where the calciner separator comprises a solid-gas separation unit; thefuel reactor fluidly connected to the calciner separator, where the fuelreactor operates at a fuel reaction temperature and fuel reactionpressure, where the fuel reactor comprises a fluidized bed reactor,where the fluidized bed comprises calcium carbonate; a fuel reactorseparator fluidly connected to the fuel reactor, the air reactor, and areducing reactor, where the fuel reactor separator comprises a solid-gasseparation unit; the reducing reactor fluidly connected to the fuelreactor separator and the air reactor separator, where the reducingreactor operates at a reducing pressure and a reducing temperature; anda reducing reactor separator fluidly connected to the reducing reactorand the calciner unit, where the reducing reactor separator comprises asolid-gas separation unit.
 6. The system of claim 5, wherein the fuelreaction pressure is atmospheric pressure, and further wherein the fuelreaction temperature is between 800 deg C. and 850 deg C.
 7. The systemof claim 5, wherein the air reaction pressure is atmospheric pressure,and further wherein the air reaction temperature is between 600 deg C.and 1300 deg C.
 8. The system of claim 5, wherein the calciner reactionpressure is atmospheric pressure, and further wherein the calcinerreaction temperature is between 850 deg C. and 950 deg C.
 9. The systemof claim 5, wherein the reducing pressure is atmospheric pressure, andfurther wherein the reducing temperature is between 650 deg C. and 700deg C.
 10. A system for recovering sulfur from a tail gas stream, thesystem comprising: a sulfur recovery unit, the sulfur recovery unitconfigured to produce a tail gas stream and an elemental sulfur streamfrom an acid gas stream; and a chemical looping combustion (CLC) unitfluidly connected to the sulfur recovery unit, the CLC unit configuredto produce a product effluent, the product effluent comprising calciumsulfate.
 11. The system of claim 10, wherein the CLC unit comprises thesystem according to claim
 1. 12. The system of claim 10, wherein the CLCunit comprises the system according to claim
 5. 13. The system of claim10, further comprising: a gas sweetening unit fluidly connected to thesulfur recovery unit, the gas sweetening unit configured to produce theacid gas stream from a sour gas stream, where the sour gas streamcomprises hydrogen sulfide, product gases, and combinations of the same.14. The system of claim 10, further comprising: a gas sweetening unitfluidly connected to a membrane unit, the gas sweetening unit configuredto produce the acid gas stream from a sour gas stream, where the sourgas stream comprises hydrogen sulfide, product gases, and combinationsof the same; and a membrane unit fluidly connected to the gas sweeteningunit, the membrane unit configured to produce a hydrogen sulfide richacid gas from the acid gas stream, where the hydrogen sulfide rich acidgas is introduced to the sulfur recovery unit such that the tail gasstream is produced form the hydrogen sulfide rich acid gas.